Harry is a 77-year-old male physician with a long history of type 2 diabetes and chronic kidney disease (stage 3b) among other medical problems. His eGFR is 25-30 and his urine albumin to creatinine ratio (UA/Cr) is over 300 mg/g, which indicates chronic kidney disease. He is on two medications that protect his kidneys – Kerendia and Farxiga – and he’s being seen by a nephrologist. He also takes Trulicity for his diabetes.
Harry’s 30-day FreeStyle LibreView Download Data:
As you can see from the download, Harry’s time in range is excellent – above 90% (goal above 70%) and without hypoglycemia! His glucose variability is less than 20% (goal less than 37%). His estimated A1c (referred to in the report as GMI or glucose management indicator) is 6.8%.
When I ordered Harry’s laboratory work, his A1c came back at 4.9%, which is much lower than you’d expect for the blood sugars that are documented on his CGM report.
It’s well known that chronic kidney disease and anemia (which goes along with CKD) can give someone a falsely low A1c. This is why time in range and another CGM metric such as GMI (or estimated A1c) are so important, because those glucose levels are not affected by chronic kidney disease as the A1c is.
There’s a whole list of other medical conditions that can give inaccurate A1c levels, such as pregnancy, sickle cell trait, liver disease, and being part of certain ethnic groups. See the list below for the many conditions that can affect an A1c result:
How Laboratory Blood Work Is Affected by CKD
People with CKD are anemic. The A1c measures glucose bound to red blood cells, and if you’re anemic you don’t have many red blood cells so you’re measuring the glucose bound to a fewer number of red blood cells. Anything that causes anemia will cause a falsely low A1c, which can be very misleading and lead to inappropriate insulin management decisions. A lot of doctors, quite frankly, miss it. Harry’s low A1c would fool many doctors who aren’t knowledgeable about the relationship between chronic kidney disease and the accuracy of the A1c test.
People with CKD or any condition that causes anemia need to know that their A1c may not be accurate. It’s not uncommon for people with poor glucose control (like an estimated A1c of 8.5 or higher on their CGM) to get a lab A1c result of 6.9 and then their doctor pats them on the back and tells them they’re doing great. The A1c used to be all we had to judge long-term diabetes control, but the availability of CGM devices and the metrics they can provide really uncover the pitfalls of the A1c test.
My patient Harry is actually doing really well diabetes-wise, based on his CGM. There are a lot of reasons why an A1c may be inaccurate, and that’s why time in range and estimated A1c or GMI from a CGM are much better indicators of long-term glycemic control.